The present invention relates to methods for forming ordered nanometer-scale arrays of metal or semiconductor junctions on a semiconductor surface by means of xe2x80x9cnatural lithographyxe2x80x9d.
Decreasing size is the current trend in electronic device fabrication. The present invention provides devices with nanometer-scale features and methods of producing these features that are more efficient and less costly than other techniques. The production of massively parallel arrays of metal-semiconductor and semiconductor-semiconductor junctions is potentially of use in a variety of electronic devices, including, but not limited to, diodes, solar energy collectors, quantum dot structures, substrates for surface enhanced Raman spectroscopy, ultramicroelectrodes, and computer memory.
Producing well-defined nanostructures smaller than about 100 nm may require the development of techniques beyond optical lithography. Although conventional beam lithography techniques are capable of such resolution, they often rely on an electron or ion beam rastered over a surface to create features in the lithographic mask. Metal is then deposited through the mask features onto the substrate surface. The use of a beam to fabricate a mask requires expensive equipment and has a low throughput, since features are often be formed one at a time (i.e., in a serial fashion).
xe2x80x9cNatural lithographyxe2x80x9d refers to a technique in which a crystalline colloid mono- or bilayer is assembled on the surface of a substrate to form a lithographic mask. A second material is deposited through the spaces between the assembled colloidal particles onto the surface of the substrate. The size and geometry of the features created is dependent on the size and arrangement of the colloid particles.
Natural lithography has been employed in the past to form structures on glass surfaces, mica, or on silicon surfaces having a significant oxide layer (i.e., a layer that is at least about 30 xc3x85 thick). Due to the importance of wetting the surface on which the lithographic mask is to be formed, many of these demonstrations of natural lithography have employed surfactants and other wetting agents that leave chemical residues on the substrate. Additionally, another common method of forming a colloidal mask, spin-coating, yields colloidal formations that have small regions of crystallinity interspersed with large regions of disorder. Spin-coating has therefore not thus far proven useful for forming macroscopically large regular arrays of features on surfaces.
The fabrication of electronic devices such as semiconductor diodes requires a clean silicon surface that is essentially free of oxide (i.e., it contains a layer of oxide that is less than 30 xc3x85 thick) and that is also free of chemical residue from surfactants or other wetting agents. The present invention provides, among other advantages, a method of forming large ordered arrays of nanoscale features on a clean semiconductor surface without leaving undesirable chemical residues in the resulting product. The method is capable of producing arrays covering many square mm or more of the substrate""s surface. In addition, the present invention allows formation of features that are much smaller than those possible via optical lithography and is appreciably more efficient than beam techniques, since the lithographic mask is produced in a parallel rather than a serial process.
The method of the present invention for forming a periodic array of nanoscale features on a semiconductor surface includes etching the semiconductor surface to render the surface hydrophilic. Forming a crystalline colloid mono- or bilayer on the etched surface, and depositing a material through the colloid layer onto the substrate surface. The material to be deposited can be any suitable material including, for example, a semiconductor or a metal. The crystalline colloid layer is formed by withdrawing the substrate from a sol of the colloid particles. Preferably, the formation of the crystalline colloid layer is accomplished in an inert atmosphere. After the deposition of the material, the colloid layer is removed.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.